JP4725025B2 - Method for producing laminated metal plate for can lid - Google Patents

Description

The present invention relates to a method for producing a laminated metal plate that is used as a can lid material for beverage cans, food cans, and the like, and is particularly suitable for an easy open end type can lid.

  In recent years, the resin coating of can materials has been laminated, and for example, for beverage cans, the bottom and can body of a two-piece can and the can body of a three-piece can have been laminated. Reasons for the lamination of can materials in this way include rationalization of manufacturing processes by omitting painting and baking, lower environmental impact by omitting solvent drying processes (baking processes), and inclusion in paints And avoidance of elution of environmental hormones such as BPA. In particular, regarding environmental hormones, there is a report that a very small amount of BPA affects the human body. In general, food cans have more BPA elution than beverage cans, and it is expected that laminating will continue in the field of food cans.

However, in the actual market, for example, in the case of beverage cans, the lamination of the bottom part of the two-piece can and the can body part is proceeding, whereas the lamination of the top lid and the bottom cover of the three-piece can is proceeding. Not. Similarly, food can laminate lids are not common. It is considered that the reason why the laminating of the lid material does not proceed in this way is because the problems unique to the can lid have not been solved.
There may be various reasons for preventing the laminating of the lid, but one of the most difficult issues when laminating the lid is that severe processing may be performed after the printing process. is there. In recent years, the top lid for beverage cans is mainly a steion tab type easy open end lid, and for food cans, easy open end lids that do not require can openers are increasing. Most of the easy open end type lids for food cans are printed with instructions on how to open the lid. Usually, this printing is performed before processing of the lid, and thereafter, it is formed into a lid shape (cover manufacturing). However, since heat is applied during printing in the printing process, the laminate film (resin layer) deteriorates, and the film cannot follow the processing in the subsequent lid making process, resulting in film breakage, resulting in deterioration in corrosion resistance. End up.

  As mentioned above, laminating of the lid material in the market has not progressed, but many proposals have been made on this, and this itself indicates that there is a large problem that is unresolved compared with the magnitude of demand. In particular, many proposals have been made regarding a manufacturing method of an easy open-end lid that does not require repair coating, which is considered to be the biggest problem, and a laminated steel sheet for the lid used therefor. For example, in Patent Document 1, the polyester resin is applied only to the inner surface side to achieve non-repair of the inner surface. However, this method requires not only the exterior surface to be repaired, but also does not take into account film degradation due to the printing process after lamination, and is not applicable to lids that are printed after lamination. difficult.

Patent Document 2 discloses an easy-to-end easy-open-end lid film in which the degree of biaxial orientation of the polyester film is controlled, but this also takes into account the deterioration of the film due to the printing process after lamination. Not. In addition, the biaxially oriented film has no provisions regarding the state after lamination, despite the fact that the orientation state after lamination largely dominates the properties, and a specific lid-making method such as a score processing method is also specified. It has not been.
In addition, Patent Document 3 and Patent Document 4 define film physical properties (such as plane orientation) after lamination, and there are disclosures that take into consideration the workability after heat treatment. The lid making method is not specified, and according to the investigation by the present inventors, it has been found that sufficient corrosion resistance cannot be obtained when general score processing is performed. Furthermore, Patent Document 5 has provisions relating to a score processing method and a resin film, but this also does not take into account deterioration of the film due to a printing process after lamination.

JP 2001-122258 A JP-A-9-309146 JP-A-5-77358 JP-A-5-77359 JP 2000-301268 A

  When the plate thickness distribution after the lid making process in the easy open end lid was examined, the largest change in the plate thickness occurred in a portion of a breaking groove called a score (hereinafter referred to as a score portion). This score part is usually repaired by repair coating, but there is also a method of avoiding repair coating by devising the score processing method and the configuration of the laminated steel plate as disclosed in Patent Document 5 and the like. However, according to the results of the investigation by the present inventors, even if the film (resin layer) breakage at the score part is eliminated by using a specific laminated steel sheet and the score processing method, the film breaks at other processed parts. Has been found to occur. When the rupture site was examined in detail, the film rupture occurred on the yama side of the locally bent processed portion, where there was almost no change in the plate thickness. In lid manufacturing, it is widely used to provide bent parts (for example, beads and embosses) in the flat plate part (panel part) for the purpose of increasing the rigidity of the lid or absorbing surplus due to score processing. However, it has been found that film breakage tends to occur on the yama side of the processed part with such bending deformation even if the degree of processing is slight. This phenomenon is a peculiar phenomenon seen in laminated steel sheets after heat treatment (for example, laminated steel sheets baked in the printing process after lamination), and is clearly different from the processing behavior of unheated laminated steel sheets. understood. Therefore, it is considered that the processing characteristics after the heat treatment are indispensable for the lid material that requires the printing process, and a coating film specific to the lid corresponding to this is necessary. Hereinafter, this special processing is referred to as “local bending processing”, and other processing is referred to as “general processing” to be distinguished.

The object of the present invention is a laminated metal for can lids that is excellent not only in general processability such as score processing but also in local bending performed after heat treatment when applied to an easy open end type can lid material. It is providing the manufacturing method of the laminated metal plate for can lids which can manufacture a plate stably .

  As mentioned above, it was thought that the film breakage in the local bending part of the laminated steel sheet was caused by the deterioration of the film during heat treatment, so the cause was used by using the laminated steel sheet of polyethylene terephthalate resin or polybutylene terephthalate resin. Detailed investigation and examination were conducted. As a result, in the laminated steel sheet using these resins, it was found that spherulites were generated in the film during the heat treatment. In general, it is known that when spherulites are formed, the film becomes brittle, and the formation of such spherulites degrades the film, and the film is broken during lid-making after heat treatment (printing process). Estimated. Further, it has been found that even if the baking conditions in the printing process are slightly changed, it is difficult to suppress the formation of spherulites in general polyethylene terephthalate resins and polybutylene terephthalate resins.

  Therefore, the present inventors have made the following investigations in order to obtain a film structure that can be made with a lid without causing film breakage even when spherulites are formed. In the laminated steel sheet of polyethylene terephthalate resin, since it is known that the degree of crystal orientation has a great influence on the film properties, the present inventors first used a single-layer biaxially stretched polyethylene terephthalate film and laminated conditions Various changes were made to laminate steel sheets having various crystal orientations, and the investigation was conducted. In this investigation, a heat treatment equivalent to the printing baking process was applied to the laminated steel sheet, and then an easy open-end lid was formed to examine workability (corrosion resistance). As a result, it was found that a high degree of orientation shows a good result for the local bending workability in question. In general processing, the lower the orientation, the better the workability, but in this local bending, the opposite result was obtained. This means that if the processing of the lid is only the local bending process in question, or if the processing level is sufficiently small even when other general processing is involved, the degree of orientation is appropriately set by the above-described method. This means that lid molding is possible. In fact, it has been found that there are cases where this coating design can adequately handle the bottom lid. However, the present invention is not intended to cover materials with such a processing level, but to process under severe processing conditions such as local open processing and general processing with a large degree of processing, such as an easy open end cover. It is also intended for lids to which a non-repair type score processing with a high degree of processing (for example, score processing using a curved mold) is applied.

  Except for the local bending part, especially difficult parts in the lid making process of the easy open-end lid, when applying non-repair type score processing (for example, score processing with a curved die), the score processing part and rivet processing Part. The effect of spherulite generation by heat treatment is not negligible for score processing, but the effect of the amount of oriented crystals is still much greater. Therefore, the score processing can be sufficiently handled by appropriately setting the amount of oriented crystals. The rivet processing portion is a processing portion to which rivet processing (processing to crush the overhang portion) is applied after the overhang processing is performed. The overhanging process shows the same tendency as the score process, and can be handled by appropriately setting the amount of oriented crystals. In general, it can be said that the processing is easier than the score processing. On the other hand, in the subsequent rivet processing, since an element of bending is added, the influence of spherulite generation by heat treatment cannot be ignored. However, the degree of processing tends to be lighter than the deformed portion of local bending. Therefore, the rivet processing has both a general processing element and a local bending process element, but it can be said that it is a mild process compared to the processing of the score part and the local bending part.

On the other hand, the effect of spherulites is very large for local bending. For this reason, even if the amount of oriented crystals is adjusted by simply controlling the laminating conditions, it is impossible to achieve both the workability of the severely processed portion and the locally bent portion as described above.
As described above, general processing is better as the amount of oriented crystals in the film is lower, and conversely, local bending is better when the amount of oriented crystals is somewhat higher. From the viewpoint of the amount of crystals, it can be said that it is a reciprocal characteristic. Therefore, the amount of oriented crystal should be designed to an optimum value that satisfies both characteristics, but there is no optimum area for an easy open-end lid or the like that requires a printing process. There is no drastic measure to improve both characteristics other than quantity.

  Therefore, the present inventors paid attention to the distribution in the film thickness direction of the amount of oriented crystals. Polyethylene terephthalate monolayer film laminated by a normal laminating method has an amorphous layer (or a layer close to amorphous) called a melt layer in the vicinity of the steel plate side, and an oriented crystal region on the surface layer side through a transition region. Existing. It is known that the birefringence measured by a method such as the retardation method has a correlation with the amount of oriented crystals, and when examining the change of the birefringence in the film thickness direction, Shows a melt layer having a low birefringence, and then a transition region in which the birefringence increases as the distance from the steel plate increases. Next, the oriented crystal region where the birefringence does not change so much occupies the surface layer. The ratio of the thicknesses of these layers depends on the lamination conditions, but is generally composed of a 10 to 20% melt layer, a 10 to 20% transition layer, and a 60 to 80% oriented crystal layer. Therefore, in a polyethylene terephthalate-based single layer film laminated by a normal laminating method, the oriented crystal layer occupies a large volume ratio.

  In the formation of can lids, general processing parts (for example, non-repair-type score processing parts) excluding local bending parts are processing places with large deformations, but in the polyethylene terephthalate-based single layer film as described above, In such a processed portion, the oriented crystal layer that is disadvantageous in workability and occupies a large volume ratio is forced to undergo great deformation. Of course, it is possible to reduce the crystal amount of the oriented crystal layer by lowering the total amount of oriented crystals, and to improve the workability of this part, but in that case, the local bending workability deteriorates. become.

  On the other hand, the local bending process is a small process with almost no change in the plate thickness, and the entire film is not forced to undergo a large deformation. However, when spherulites are generated by heat treatment or the like, the film becomes brittle, and the film breaks on the yama side of the processed part during local bending. In a film having a large amount of oriented crystals, the oriented crystal part is rich in elasticity, and it is considered that the stress of bending deformation can be relaxed in this part, so that the film does not break. However, when the amount of oriented crystals decreases, the stress cannot be relaxed, resulting in film breakage. According to the inventors' investigation, it has been found that the amount of oriented crystals is dominant with respect to local bending, but the position where the crystals exist may not significantly affect the bending.

  From the above investigation results, the present inventors have come up with one idea. The idea is that a high orientation crystal layer can be placed only on the thin surface layer, and a thick low orientation crystal layer rich in general workability can be placed underneath it, satisfying both characteristics (local bending workability and general workability). It can be done. That is, this film structure is a structure in which the majority of the film is a low-orientation crystal layer that is rich in general workability, and an orientation crystal layer that relaxes local bending is present only in the thin upper layer part. Even if the upper layer portion does not follow the deformation in general processing, unless the lower layer portion occupying most of the film does not break, the entire film does not break, whereas in local bending, the orientation of the upper layer portion The crystal layer can alleviate deformation.

As a result of experiments and examinations based on the above ideas, the above-described processing characteristics can be realized by forming a film structure in which the birefringence of the upper layer portion and the lower layer portion having a specific thickness is controlled within a predetermined range. I understood.
Moreover, in order to realize such a film structure, it has been found that a method utilizing the difference in melting point of the film is appropriate. That is, a film having oriented crystals can be obtained by superimposing and stretching two layers having different melting points by a co-extrusion method or the like. When this film is laminated by a general heat fusion method, a layer having a low melting point is obtained. Since the oriented crystals start to melt first, a laminate film having a special structure having an upper layer portion with a large amount of oriented crystals and a lower layer portion with a small amount of oriented crystals can be obtained by controlling the laminating method.

The present invention has been made on the basis of the above knowledge, and is obtained by condensation polymerization of terephthalic acid or a dicarboxylic acid component composed of terephthalic acid and isophthalic acid and a diol component composed of ethylene glycol on at least one surface of the metal plate. A laminate metal plate having a resin film composed of at least one polyester resin selected from ethylene terephthalate-ethylene isophthalate copolymer and polyethylene terephthalate, in which the repeating unit composed of ethylene terephthalate is 85% or more by mole ratio. The resin film has an upper layer portion having a thickness of 1 to 4 μm having a birefringence of 0.055 to 0.070 and a lower layer portion having a thickness of 10 to 25 μm and a birefringence of 0.035 or less. Or the resin film has a thickness of 1 to 4 having a birefringence of 0.055 to 0.070. It consists of an upper layer part of μm, an intermediate layer part having a thickness of 5 μm or less having a birefringence of more than 0.035 and less than 0.040, and a lower layer part having a thickness of 10 to 25 μm having a birefringence of 0.035 or less. A method for producing a laminated metal plate for a can lid, comprising a biaxially stretched polyester bilayer film comprising a high melting point upper layer resin and a low melting point lower layer resin, wherein the upper layer resin and the lower layer resin have a melting point difference of 10 ° C. or more A method for producing a laminated metal plate for can lids, wherein a resin film is formed by laminating a metal plate by thermocompression bonding.

Since the laminated metal plate for can lids manufactured according to the present invention has a coating structure composed of a lower layer portion that satisfies general processability such as rivet processing and score processing and an upper layer portion excellent in local bending workability, When applied to an easy open end type can lid material, excellent local bending workability can be obtained without substantially impairing general workability. For this reason, even when the lid is processed through the printing process, a can lid having excellent corrosion resistance can be produced without causing film breakage.
According to the method for producing a laminated metal plate for can lids of the present invention, the laminated metal plate having the above-described film structure can be produced stably .

The laminated metal plate for can lids of the present invention has a resin film made of a polyester resin on at least one surface of the metal plate, and this resin film has a birefringence of 0.040 to 0.070 in thickness 1. It consists of an upper layer portion of ˜4 μm and a lower layer portion having a thickness of 10 to 25 μm having a birefringence of 0.035 or less, and the birefringence between the upper layer portion and the lower layer portion is more than 0.035 and less than 0.040 An intermediate layer portion (transition layer) having a thickness of 5 μm or less may be present.
Here, the upper layer part, the lower layer part, and the intermediate layer part of the resin film are defined by the distribution of the birefringence of the film after lamination. Therefore, the distinction between these layer parts is the resin film before lamination. It does not correspond to the layer structure (for example, upper layer, lower layer).

The reason why the resin film to be laminated is the polyester resin is that the polyester resin can secure the local bending workability and the general workability in the most balanced manner.
As the polyester-based resin, a polyethylene terephthalate-based resin is preferable because it has a good balance of elongation and strength with respect to processing and is suitable for food hygiene. In lid processing, it is desirable that the film has a good balance between extensibility and strength. However, in general, elongation and strength are contradictory properties. When the elongation is good, the strength is low, and when the strength is high, the elongation tends to be poor. Among resins suitable for food hygiene, polyethylene terephthalate polyester resin is excellent in the balance between elongation and strength for lid processing.

Specifically, the polyester resin is obtained by polycondensation of a dicarboxylic acid component composed of terephthalic acid or / and isophthalic acid and a diol component composed of ethylene glycol, and the repeating unit composed of ethylene terephthalate has a molar ratio of 85%. or in which ethylene terephthalate - ethylene isophthalate copolymer, it is preferable to use at least one member selected from poly ethylene terephthalate.

  When the thickness of the upper part of the resin film exceeds 4 μm, the general workability is inferior. On the other hand, when the thickness is less than 1 μm, the local bending workability is inferior. Moreover, the balance of local bending workability and general workability can be made more favorable by the thickness of an upper layer part being 2 micrometers or less. Although it is desirable that the intermediate layer is not ideally present, it is acceptable if the thickness is 5 μm or less. If the intermediate layer portion is thicker than this, the general workability deteriorates. If the thickness of the lower layer is less than 10 μm, the general processability is inferior. On the other hand, if it exceeds 25 μm, the film thickness increases and the cost increases.

The birefringence has a correlation with the amount of oriented crystals. When the birefringence of the upper layer is less than 0.040, the local bending workability is inferior. On the other hand, when it exceeds 0.070, the general workability is inferior. Moreover, the balance of local bending workability and general workability can be made more favorable by making the birefringence of this upper layer part into 0.055-0.070 especially.
The reason why the birefringence of the lower layer portion is defined as 0.035 or less is that the lower layer portion is basically more advantageous as it is closer to amorphous. However, even if the lower layer portion is not completely amorphous, the desired effect can be obtained if it is 0.035 or less. Also, the birefringence may not be 0 even if it is not in a clear crystal state (it is considered that the orientation has an effect), and it is more effective to specify the birefringence as 0.035 or less. is there. That is, in the present invention, if the birefringence is 0.035 or less, it may be substantially amorphous. In order to keep the birefringence of the upper layer within the above range, it is advantageous that the birefringence of the lower layer has an allowable range (allowable range of 0.035 or less). It is good to design appropriately in the range.

The resin film laminated on the metal plate may be composed only of a resin film in which the amount of oriented crystals is controlled in the film thickness direction as described above. However, other resin layers ( For example, an uppermost resin layer, an adhesive layer for ensuring adhesion to a metal plate or adhesion between layers, and the like may be provided.
If necessary, the resin film may contain additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, a crystal nucleating agent, A wax component or the like can be added to the surface layer.
The resin film may be formed by a film lamination method (film sheet thermocompression bonding), or may be formed by a coextrusion method or a direct lamination method.
There is no special restriction | limiting in the base metal plate of the laminated metal plate of this invention. Tin-free steel is preferable in terms of being inexpensive and excellent in adhesion, but other surface-treated steel plates such as tinplate, aluminum plates, and the like may be used.

Next, the preferable manufacturing method of the laminated steel plate for can lids of this invention is demonstrated.
In this manufacturing method, a biaxially stretched polyester bilayer film composed of a high melting point upper layer resin and a low melting point lower layer resin and having a melting point difference of 5 ° C. or higher, preferably 10 ° C. or higher is thermocompression bonded. Laminate to a metal plate.
Thus, by laminating the biaxially stretched polyester bilayer film in which the upper layer resin and the lower layer resin have a predetermined melting point difference, the above-described oriented crystalline resin film can be obtained. In addition, it is more preferable to select a resin having a melting point difference of 10 ° C. or higher between the upper layer resin and the lower layer resin because the degree of freedom in constraints on the lamination conditions is greatly improved.
Further, the thickness of the intermediate layer, that is, the birefringence transition region can be controlled by a laminating method. That is, by raising the laminating temperature and shortening the rapid cooling time at the time of thermocompression bonding (and after thermocompression bonding), the transition region becomes thinner, and conversely, if it is made longer, the transition region becomes thicker. By appropriately selecting these conditions, The thickness of the birefringence transition region can be adjusted.

Next, a method for producing a can lid using the laminated metal plate of the present invention will be described.
When manufacturing a can lid using the laminated metal plate of the present invention, especially when manufacturing a can lid that does not require repair coating, the score portion with the largest plate thickness change is processed by the following specific method. It turned out to be preferable.
That is, in the lid making process, it is desirable to perform score processing using a curved mold having a radius of curvature R at the tip of 0.1 to 1.0 mm. If the radius of curvature of the curved mold is too small, the film may be broken due to insufficient strength. On the other hand, if the radius of curvature is too large, the degree of processing tends to be large, and molding tends to be difficult. In the above-described score processing using a curved mold having a tip radius of curvature R of 0.1 to 1.0 mm, for example, one of a pair of upper and lower molds has a tip radius of curvature R of 0.1 to 1. When the curved mold is 0.0 mm and the other is a flat mold, the pair of upper and lower molds are both curved molds having a tip radius of curvature R of 0.1 to 1.0 mm, etc. Any of these may be used, and the fracture groove is formed by press molding with such a mold.

As the base metal plate, a tin-free steel original plate having a thickness of 0.20 mm and a hardness of T4 was used. The base metal plate was laminated with a resin film using a film laminating method by thermocompression bonding to produce a laminated steel plate for a can lid.
A method for measuring the birefringence of the obtained laminated steel sheet and a method for evaluating lid-making characteristics are shown below.
(1) Measurement of birefringence The birefringence in the film thickness direction was measured by a retardation method.

(2) Lid making property evaluation The laminated steel plate was heat-treated at 210 ° C for 10 minutes, and then subjected to easy open-end lid making. The score part was a non-repair type score process, and was molded using a 0.3 mmR curved mold. The score processing is performed under two conditions: the thinnest plate thickness is 50 μm and the condition is 60 μm. The local bending is performed with a bending die tip curvature of 1.5 mmR and 1.0 mmR 2. Performed under conditions.
The corrosion resistance of the locally bent portion, the rivet portion, and the score portion of the formed lid was evaluated. Corrosion resistance is evaluated by measuring the current value when applying a voltage of 6.0 V with a sponge containing an electrolytic solution in close contact with the measurement part of the processed part of the lid after the lid making process. Based on the evaluation. In addition, as electrolyte solution, what added 2 drops of surfactant to 200 mass of 1mass% KCl aqueous solution was used.
In the score processing section, even when the thinnest plate thickness is 50 μm, “◎” if the current value is 0.1 mA or less, and when the thinnest plate thickness is 50 μm, the current value exceeds 0.1 mA, but when the thinnest plate thickness is 60 μm, When the value was 0.1 mA or less, “◯” was given, and when the thinnest plate thickness was 60 μm, the current value exceeding 0.1 mA was taken as “x”. In local bending, even when the mold tip curvature is 1.0 mmR, the current value exceeds 0.1 mA when the current value is 0.1 mA or less. When the mold tip curvature is 1.0 mmR, the current value exceeds 0.1 mA. When the mold tip curvature was 1.5 mmR, the current value was 0.1 mA or less, and when the mold tip curvature was 1.5 mmR, the current value exceeded 0.1 mA was rated as “X”. In the rivet processing, when the current value was 0.1 mmA or less, “◯” was given, and when the current value exceeded 0.1 mA, “x” was given.

Tables 1 and 2 show the film configuration of the laminated steel sheet of each example, and Table 3 shows the results of lid-making characteristics evaluation of each example.
Invention Example 1 is an ethylene terephthalate-ethylene isophthalate copolymer in which the upper layer portion is polyethylene terephthalate and the lower layer has a different copolymerization ratio, and the birefringence of the upper layer portion is in a preferable range of 0.058. Excellent corrosion resistance is obtained in both the score processing section and the local bending section .
Inventive examples 2 and 3 are obtained by changing the thickness of the upper layer part, but the corrosion resistance of any processed part is also good. In invention example 3 where the thickness of the upper layer part is thick, the corrosion resistance of the locally bent portion is particularly excellent, and in invention example 2 where the thickness of the upper layer part is thin, the corrosion resistance of the score processing part is particularly excellent.

Inventive Examples 4 and 5 are obtained by changing the thickness of the lower layer part, but Inventive Example 4 in which the lower layer part is thick has particularly excellent corrosion resistance at the score processing part and the local bending part.
In Invention Example 6, the birefringence of the upper layer is high and the thickness of the intermediate layer portion is controlled to be thin, but excellent corrosion resistance is obtained in both the score processing portion and the local bending portion.

In Comparative Examples 1 and 2, a two-layer film in which the melting point difference between the upper layer resin and the lower layer resin is 3 ° C. is laminated, both of which have a small difference in birefringence between the upper layer portion and the lower layer portion. The birefringence of the lower layer part deviates from the conditions of the present invention, and in Comparative Example 2, the birefringence of the surface layer deviates from the conditions of the present invention because the difference in melting point between the upper layer and the lower layer is small. As a result, Comparative Example 1 is inferior in corrosion resistance in the score processing part and rivet processing part, and Comparative Example 2 is inferior in corrosion resistance in the local bending part and rivet processing part.
In Comparative Example 3, although the birefringence of the upper layer portion satisfies the conditions of the present invention, the corrosion resistance at the locally bent portion is inferior because the upper layer portion is thin.
In Comparative Example 4, since the upper layer portion is too thick, the corrosion resistance at portions other than the locally bent portion is inferior.

Comparative Example 5 is an example using a polyethylene terephthalate single layer film, but has a coating structure in which the upper layer portion is thick and the lower layer portion is thin. Similarly, Comparative Example 6 is an example in which a polyethylene terephthalate single layer film is used, but conversely, there is no upper layer portion, and the structure has only an intermediate layer portion and a lower layer portion. For this reason, in these comparative examples, the corrosion resistance of a local bending process part and a score process part is not compatible.
Although the comparative example 7 is an example which made the lower layer part polypropylene, since a polypropylene has weak intensity | strength compared with polyester, both a score process part and a rivet process part are inferior in corrosion resistance. In addition, film breakage due to insufficient strength was observed.
Comparative Example 8 is an example in which both the upper layer part and the lower layer part are olefins. However, like Comparative Example 7, the corrosion resistance of all processed parts is inferior due to insufficient strength.
Comparative Example 9 is an example using a two-layer film in which the lower layer resin has a higher melting point than the upper layer resin, and although the corrosion resistance in the score processed portion is particularly excellent, the corrosion resistance in the locally bent portion and the rivet processed portion is Inferior.

Claims (1)

It is obtained by condensation polymerization of terephthalic acid or a dicarboxylic acid component consisting of terephthalic acid and isophthalic acid and a diol component consisting of ethylene glycol on at least one side of the metal plate, and the repeating unit consisting of ethylene terephthalate is 85% or more by mole percentage. A laminated metal plate having a resin film made of at least one polyester resin selected from an ethylene terephthalate-ethylene isophthalate copolymer and polyethylene terephthalate, wherein the resin film has a birefringence of 0.055. It consists of an upper layer portion having a thickness of 1 to 4 μm and a lower layer portion having a thickness of 10 to 25 μm and a birefringence of 0.035 or less. An upper layer portion having a thickness of 1 to 4 μm which is 055 to 0.070, and a birefringence of more than 0.035 and 0.040 An intermediate layer portion thickness of less than 5μm is fully, a manufacturing method for a can lid laminated metal sheet including the lower portion of the thickness of 10~25μm birefringence is 0.035 or less,
Resin film by laminating a biaxially stretched polyester bilayer film composed of a high melting point upper layer resin and a lower melting point lower layer resin, and having a melting point difference of 10 ° C. or more between the upper layer resin and the lower layer resin to a metal plate by thermocompression bonding A method for producing a laminated metal plate for can lids, characterized in that